Fault indicator device for amplifier tubes



March 28, 1 944. H. J. FRUNDT ET AL 2,345,042

' FAULT INDICATOR DEVICE FORAMPLIFIER TUBES Filed Nov. 13, 1940 2 ml. A4

2& 3

INVENTQRS n HANSJDAC/l/ FRI/N07 Brill/Flag IVFFLO M,

ATTORNEY Patented Mar. 28, 1944 UNITED FAULT INDICATOR DEVICE FOR AMPLIFIER TUBES Hans Joachim Friindt and Wilhelm Schiinfeld, Berlin, Germany; vested in the Alien Property Custodian Application November 13, 1940, Serial No. 365,560 In Germany September 18, 1939 2 Claims.

It is often desirable in practice to have available ways and means designed for automatic indication of tube defects. Such an arrangement would be particularly valuable and useful where equipment and outfit is concerned which comprises a large number of tubes.

What is employed for this purpose according to the invention is a circuit organization in which the failure of the emission current, upon a tube being rendered defective or inoperable, causes an indicator device to respond.

The drawing shows an exemplified embodiment of the invention. The problem here is to check up on the tube R permanently. To this end the high potential required for the operation of an electrode impressed with a positive bias is impressed upon this electrode across a resistance 2. The latter is of such a size that a considerable drop of potential is caused across it.

In parallel relation to the source of potential supply is a voltage divider comprising the resistances 4 and 5. The telltale glow tube 3 is connected between the lead connecting the resistance 2 to the electrode l and the lead connecting resistances 4 and 5. In other words, the glowtube or gaseous-conducting tube has one pole at the electrode potential. It is impressed through the voltage divider 4, 5, with a voltage which is considerably lower than the striking voltage. If, then, a tube defect arises so that the circuit to the electrode is broken the drop of potential across resistance 2 becomes zero. As a result the glow-tube 3 receives a potential which is far above the firing or striking potential. As a result the glow-tube 3 is caused to flash. The resistances may be readily proportioned so that the voltage change will be 50 volts and over, thus, insuring safe and dependable indication or telltale action. Since a current will flow through the glow-tube only when the lamp has been struck the operation of the tube will not be impaired by this glow-tube.

The new arrangement, in spite of the limited circuit means which it requires insures permanent and uninterrupted control, and the latter in no way afiects normal operations. The resistances of the glow-tube may be so chosen that most widely varying conditions can be met. If desired, the current which flows through the glow-tube may be utilized to cause actuation of another warning signal or alarm or an acoustic nature, say, a signal bell.

Where large installations of tubes are dealt with, all tell-tale glow-tubes may be united to form a panel so that such defects as may arise can be discovered immediately.

We claim:

1. In amplifying apparatus, an electronic tube having a cathode and at least one electrode which is adapted to be maintained at a high positive potential with respect to the cathode, an electrode circuit comprising a source of voltage supply and a resistance in series connected between said electrode and said cathode whereby current flowing in said electrode circuit causes a drop of potential across said resistance, a voltage divider connected across said source and in series with said resistance, a breakdown indicator glow tube consisting of two cold electrodes connected between said electrode and a point of said voltage divider, the inter-electrode space of the glow tube being in shunt with said resistance and a predetermined portion of said divider whereby the drop of potential across said resistance prevents the glow tube from firing under normal operating conditions of said tube zero potential drop across said resistance, caused by a break in the said electrode circuit, resulting in said glow tube having applied thereto a potential far above its firing potential.

2. In an electronic tube circuit of the character described wherein it is desirable to indicate the operation of a tube having a cathode and grid circuit, a bridge circuit comprising, a voltage divider formed by two resistances connected in series across a source of direct current and forming two legs of the bridge, a series resistance unit connected in series with the cathode and grid circuit of the tube across said source of direct current whereby said series resistance unit and said cathode and grid circuit form the other two legs of the bridge, and means responsive to an unbalancing of the circuit connected between the juncture of said two resistances and the juncture of said resistance unit and said cathode and grid circuit whereby the stoppage of the electron flow through the tube causes a voltage to .be impressed across said last-named means of suflicient magnitude to operate said means.

HANS JOACHIM FRUNDT.

WILHELM scnomm. 

